In recent years, the luminous efficiency of an LED is improved and a bulb-type LED lamp for general illumination or decoration is provided. In the bulb-type LED lamp, an LED module on which a plurality of LED devices are mounted and a translucent cover that covers the module are attached to the tip side of a case and light radiated from the LED devices is emitted to the outside, and a base is attached to the base end side of the case via an insulating cover made of a synthetic resin. Since the light output or life of the LED device is reduced at a temperature of 90 degrees or more, a temperature of 50 degrees or less is considered to be appropriate. In addition, a power supply circuit board for the LED accommodated in the case also has a heat-emitting element such as a capacitor or the like, and it is known that, when the temperature of the power supply circuit abnormally rises, there is a possibility that the operational reliability and the life of the circuit are impaired.
To cope with this, in a conventional bulb-type LED lamp, in order to prevent the increase in the temperature of the LED device or the power supply circuit, there is adopted a structure in which a metal heat dissipation portion is provided in a part of a case and heat conducted from the LED device or the power supply circuit is dissipated to the outside (e.g., see Patent Document 1). As the structure of the heat dissipation portion, for example, there are proposed various types each in which there is used an aluminum die cast heat sink formed with a heat dissipation fin having a plurality of grooves on its outer surface, an aluminum plate is placed on the heat sink, and an LED module is disposed on the aluminum plate (see, e.g., Patent Documents 2 to 5).
However, since the conventional heat dissipation portion uses a casting obtained by casting of a metal material using a die, the aluminum die cast heat sink in particular, the thickness of the heat dissipation portion is large, a material cost is increased, and a reduction in weight is limited so that it has been difficult to use the conventional heat dissipation portion in a large-size lighting device. In addition, since a post process after the casting is required, production time is prolonged, and the life of the die is short so that a large-scale production facility has been required for mass production. Further, since the material is limited to a material suitable for casting, there has been a problem that the choice of the material is limited and it is not possible to freely choose a material excellent in thermal conductivity.
Patent Document 1: Japanese Patent Application Laid-open No. 2006-313727
Patent Document 2: Japanese Patent Application Laid-open No. 2009-170114
Patent Document 3: Japanese Patent Application Laid-open No. 2005-166578
Patent Document 4: Japanese Patent Application Laid-open No. 2008-186758
Patent Document 5: Japanese Patent Application Laid-open No. 2009-43694